High Pure Water Permeability Research Articles

High performance composite hollow fiber nanofiltration membrane fabricated via the synergistic effect of co-solvent assisted interfacial polymerization and macrocyclic polyamine incorporation

The necessity for high-performance thin film composite (TFC) nanofiltration (NF) membranes for drinking water and wastewater treatment is becoming increasingly apparent in the face of the global water crisis. In this work, co-solvent (acetone) assisted interfacial polymerization (CAIP) and incorporating macrocyclic polyamine (Cyclen) as an aqueous co-monomer were employed to fabricate hollow fiber (HF) NF membrane and to enhance the permeability and the selectivity, respectively, thereby overcoming the inherent trade-off effect. The effects of Cyclen and acetone on the separation performance were comprehensively investigated, and the interfacial polymerization conditions were optimized. The optimal HF NF membrane exhibits a 68.6 % increment in water permeance relative to the baseline membrane while without sacrificing the Na2SO4 rejection which is as high as 99.2 %. In particular, it exhibits a superior high pure water permeability of 222.5 L m−2 h−1 MPa−1, ranking among the highest observed for HF NF membranes in the existing literature. Moreover, it exhibits excellent acid resistance as well as fouling resistance. This research paves a novel approach for developing high-performance HF NF membranes for water and wastewater treatment.

Green bifunctional unsaturated fatty acid modulated interfacial polymerization for augmented nanofiltration performance

Facile and precise regulation of the selective layer structure is challenging but highly crucial for the development of nanofiltration (NF) technology. In this work, we present an innovative strategy to modulate the polyamide physicochemical structure by introducing oleic acid (OA) into the organic boundary during interfacial polymerization (IP) process. As a naturally extracted product, OA is a kind of unsaturated fatty acid with a carboxylic head and a C17 alkyl chain tail. The presence of OA in organic phase allows to diminish the interfacial tension and accelerate the diffusion of piperazine (PIP) towards the organic boundary. Meanwhile, in situ reaction of OA with PIP during IP process yields organic particles that are embedded in the selective layer and alter its morphology. These two effects can result in opposite influence on membrane performance. Under the optimized OA dosage of 1 %, the MgSO4 rejection boosted from 70.8 % to 97.4 % while maintaining a high pure water permeability up to 16.4 ± 0.1 L m−2 h−1 bar−1. This improvement is closely attributed to the augmented crosslinking degree and lessened MWCO/average pore size. In comparison to the control sample, the membrane surface changed from a smooth to a clustered morphology while the film thickness increased. This is mainly caused by the embedding of organic particles into the selection layer. This advancement provides a convenient and effective method for the design of high-performance NF membranes.

Construction of PDA-PEI/ZIF-L@PE tight ultra-filtration (TUF) membranes on porous polyethylene (PE) substrates for efficient dye/salt separation

Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m−2·h−1·bar−1 (LMHB) and retention selectivity (SCR/Na2SO4 and SMB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties.

Solvent-free polyamide TFC membrane fabrication based on TMC vaporization for saline water recovery

While thin film composite (TFC) membranes have dominated the global desalination process, using large amounts of organic solvent during membrane manufacturing remains a major concern. Thus, a greener approach to prepare TFC membranes based on solvent-free trimesoyl chloride monomer vaporization is presented in this work. This study fabricated the solvent-free membranes by varying relevant parameters during the vapor interfacial polymerization (VIP) process and studied their impacts on the membrane properties. Evidently, the VIP membranes exhibited thinner polyamide layers than conventionally prepared membrane following the slow polymerization rate. This resulted in higher pure water permeability (2.93 L/m2.h.bar) than the conventional membrane (2.53 L/m2.h.bar) when both membranes were tested at 8 bar. Despite demonstrating slight decrease in salt rejection, the saline water recovery performance of VIP membrane was unaffected, as high salt rejection was unnecessary. Under the best synthesis conditions, a VIP membrane with lower salt rejection could rival the conventional membrane with a >98 % dye rejection while attaining substantially higher NaCl/dye selectivity (up to 330) than the conventional ones (68.75). Pertinently, the study findings demonstrated the potential of the solvent-free IP-fabricated TFC membrane for saline water recovery.

Hydrolysis co-deposition of bio-inspired hybrid hydrophilic network antifouling loose nanofiltration membrane for effective dye/salt separation

Nowadays, loose nanofiltration (LNF) membranes with effective filtration performance toward textile wastewater have drawn intensive attention. In this work, a high-performance LNF membrane was prepared via fast co-deposition of bio-inspired TA-based hydrophilic coating with in-situ hydrolysis of tetra butyl titanate (TBT) on polyethersulfone (PES) substrate. Various additives containing amino acid (l(+)-Arginine) and silane coupling agent (KH792) were mixed in the coating solution and researched their synergistic effects during membrane preparation. In-situ growth of TiO2 and co-deposition of TA-based coating endowed the LNF membrane with a uniformly rough hydrophilic surface. Therefore, the optimal LNF membrane showed a significantly high pure water permeability (92.9 L m−2 h−1·bar−1) with high rejection (>99.0 %) in treating negatively charged dyes including Eriochrome Black T, Congo Red, Chlorazol Black T, and Coomassie Brilliant Blue G. Meanwhile, low rejections for inorganic salts (Na2SO4: 7.9 %, NaCl: 2.5 %, MgCl2: 2.8 %, MgSO4: 7.3 %) were reached, and it kept distinguished separation performance in dealing with highly saline dye wastewater (containing 50 g L−1 NaCl and Na2SO4, respectively). Beyond that, the membrane had excellent antifouling properties with low flux decline of multiple model pollutants and stability during separation dye/salt mixture, which revealed the LNF membrane prepared promising potential in actual textile wastewater treatment.

Constructing quaternized graphene oxide filtration layer on PVDF membrane by a facile strategy via dopamine crosslinking and its performance

The increasing utilization of polyvinylidene fluoride (PVDF) ultrafiltration membranes in water treatment has necessitated the development of membranes with superior separation, antifouling performance and high pure water permeability. As a hydrophilic and antibacterial modifier, quaternized graphene oxide (QGO) has been successfully applied to improve the antifouling and antibacterial properties of the membranes simultaneously. Herein, we proposed a simple and effective strategy to fabricate a nanocomposite ultrafiltration membrane by coating the PVDF membrane surface with QGO and using polydopamine (PDA) as a “bio-glue”. The filtration followed by cross-linking method was utilized to construct a “brick-mud” structure on the membrane surface. The prepared QGO/PDA-PVDF membrane exhibited favorable separation and antifouling properties (79.5% of BSA rejection rate, 15.7% of irreversible fouling rate when filtering 0.5 g/L BSA solution, 97.2% of E. coli and 96.3% of S. aureus antibacterial rate), while maintaining a high pure water permeability of 1105.4 L.m−2.h−1.bar−1. QGO nanosheets were stably coated on the membrane surface, and the QGO/PDA-PVDF membrane prepared by this novel strategy also demonstrated application potential in the field of seawater desalination pretreatment. Besides, the possible mechanisms during modifications were also discussed. This research could serve as a reference for improving the comprehensive performance of PVDF ultrafiltration membrane through surface coating.

Towards sustainable management of end-of-life membranes: Novel transformation of end of life (EoL) reverse osmosis membranes for efficient dye/salt separation

Effective management of end-of-life (EoL) membranes is crucial for addressing environmental and economic concerns. A novel approach has been proposed in this study to transform discarded EoL reverse osmosis (RO) membranes into loose nanofiltration (NF) membranes that exhibit high flux and effective dye/salt fractionation. The proposed method involves oxidative treatment followed by a one-step co-deposition of polydopamine (PDA) and polyethylene glycol (PEG). Rigorous chemical and morphological characterization techniques have verified the successful transformation of the EoL membranes. The study's findings demonstrate the great potential of this method, as the transformed EoL membranes achieved high pure water permeability of 67 LMH/bar after only a 5-hour coating process, representing a remarkable 2.5-fold increase in permeability compared to the uncoated membrane. A 20-hour coating produced a denser film that reduced the permeability to 19 LMH/bar but increased the potential for dye/salt separation. The transformed membranes exhibited high rejection rates of dyes and ultra-low salt rejection, making them highly efficient for dye/salt separation. Moreover, the enhanced hydrophilicity of the transformed membranes inhibited foulant accumulation, resulting in excellent fouling resistance with a flux recovery ratio of 93.6 %. This novel approach offers a promising solution for treating dye-contaminated wastewater and promoting circular economy in membrane technology.

Low-temperature sintering of porous SiC ceramic membrane with industrial-grade sodium meta-aluminate as a sintering additive

Silicon carbide (SiC) ceramic membranes require high sintering temperatures (greater than 1800 °C), which consume substantial energy and increase the production costs. In this study, we report the successful preparation of a low-cost, high-performance SiC ceramic membrane at a low temperature of 800 °C using industrial-grade sodium meta-aluminate (NaAlO2) as a sintering agent. The effects of sintering temperature and NaAlO2 content on the microstructure, porosity, bending strength, pore size, and pure water permeability of the SiC membranes were investigated systematically. The results indicate that the optimal sintering temperature and NaAlO2 content are 800 °C and 10 wt%, respectively. The SiC membrane prepared under these conditions exhibited an average pore size of 2.57 μm, a porosity of 52.07%, a bending strength of 50.2 ± 0.41 MPa, and a very high pure water permeability of 103.3 m3 m−2 h−1 bar−1. Additionally, the SiC membrane prepared in this study also exhibited good chemical stability and could be used in acid and alkali environments for long periods. These results highlight the potential of SiC membranes in various applications, particularly in water treatment and filtration application. The findings of this study are useful to enrich membrane technology knowledge and guide future research and development of related technologies.

Dye sieving and dye/salt separation PEI-based loose nanofiltration membrane modified by NH2-MIL-101(Fe) and polyphenol coating

Effective dye sieving and dye/salt separation could recycle valuable resources during textile wastewater treatment. In this work, a loose nanofiltration (NF) membrane with outstanding performance was constructed with facile materials including the surface polyphenol coating and the polyetherimide (PEI) support. Firstly, the mixed matrix support membrane was prepared by incorporating Fe-based MOF NH2-MIL-101(Fe) into PEI membrane via non-solvent induced phase separation (NIPS) method, then the polyphenol coating based on vanillyl alcohol, which was the characteristic component derived from Gastrodia elata Blume, was co-deposited on the support PEI membrane, followed by the treatment of 1,3-propane sultone. In this way, the optimal loose NF membrane could have a high good pure water permeability (87.9 L·m−2·h−1·bar−1) while high dye/salt selectivity was reached (Selectivity: 58.9 for Congo Red/NaCl; 46.8 for Conge Red/Na2SO4). Moreover, a mixture of large molecule dye and small molecule dye could be sieved and the optimal loose NF membrane showed outstanding antifouling capacity with the flux recovery ratio of 85.7%, 98.1%, and 97.9% respectively for bovine serum albumin (BSA), sodium alginate (SA), and humic acid (HA), which was further analyzed and calculated by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The long-term stability during EBT/Na2SO4 mixture filtration endowed the membrane with great potential in treating textile wastewater.

Cleanable natural-sugar-alcohol-based polyester membrane for highly efficient molecular separation

Achieving zero discharge of salt-containing dye wastewater is essential for sustainable development, which requires precise separation of organic dyes and inorganic salts. This work describes a new strategy for the preparation of cleanable polyester loose nanofiltration (LNF) membranes using inexpensive natural-sugar-alcohols (erythritol, sorbitol, and maltitol) as aqueous monomers. The resulting polyester membrane has a loose structure with hydrophilic properties and negative charge density. The optimized sorbitol/trimesoyl chloride (TMC) membranes exhibited high pure water permeability (80.63 ± 1.72 L·m−2·h−1·bar−1), a high selectivity factor for salt/dye separation at 229.07(dye rejection of 99.6 ± 0.48%, salt rejection of 8.17 ± 0.8%). Moreover, Sorbitol/TMC polyester membranes exhibit excellent compatibility with dye-fouling detergents, antifouling ability, and long-term stability. The unoptimized erythritol/TMC and maltitol/TMC membranes also exhibit high water permeability and accurate dye/salt sieving ability. The results reveal that natural-sugar-alcohol-based polyester membranes are expected to stand out in the future of salt-containing dye wastewater treatment.

Ultrasound-assisted synthesis of MSNs/PS nanocomposite membranes for effective removal of Cd2+ and Pb2+ ions from aqueous solutions

Contamination of heavy metal (Cd2+ & Pb2+) ions in drinking water is producing major impacts on the environment and public health and is considered one of the greatest dangers to humanity. Membrane technology has been chosen over other processing methods due to its simplicity and high capacity for more effective removal of hazardous heavy metals. In the current study, amine, thiol, and bi-thiol functional groups were used to functionalize mesoporous silica nanoparticles (MSNs) to improve the efficiency of the silica nanoparticle. The morphology of the MSNs as well as the existence of amine and thiol on the surface of MSNs was demonstrated by a variety of characterization techniques, including FTIR, TEM, and SEM examination. The impact of surface-modified MSNs on the morphology, properties, and performance of polysulfone (PS) nanofiltration (NF) membranes was also evaluated. The membrane that incorporated amine with thiol-based MSNs (DiMP-MSNs/PS-NF membrane) had the highest pure water permeability (6.7 LMH bar−1). As a result of the functional groups, the surface-modified MSNs/PS nanofiltration are extremely effective at removing heavy metal ions from aqueous solutions. The surface-modified MSNs/PS nano-filtration membranes exhibit unprecedented Cd2+ and Pb2+ removal rates of approximately 82% and 99%, respectively. This research indicates the possible application of the surface-modified MSNs/PS nanofiltration membrane as a promising platform to remove heavy metal ions from polluted water.

Antifouling thin-film nanocomposite NF membrane with polyvinyl alcohol-sodium alginate-graphene oxide nanocomposite hydrogel coated layer for As(III) removal

Removal of As(III) from the polluted waters is a challenge. It should be oxidized to As(V) for increasing its rejection by RO membranes. However, in this research, As (III) is directly removed by a high permeable and antifouling membrane prepared through the surface coating and in-situ crosslinking procedure of polyvinyl alcohol (PVA) and sodium alginate (SA) as coating materials containing graphene oxide as a hydrophilic additive on a polysulfone support with glutaraldehyde (GA) chemical crosslinking agent. The properties of the prepared membranes were evaluated through contact angle, zeta potential, ATR-FTIR, SEM, and AFM. The addition of GO in the polymeric networks of SA and PVA hydrogel coating layers led to a better hydrophilicity and a smoother surface and a higher negative surface charge resulted in improvment of permeability and rejection of membranes. Among the prepared hydrogel-coated modified membranes, SA-GO/PSf indicated the highest pure water permeability (15.8 L m−2 h−1 bar−1) and BSA permeability (9.57 L m−2 h−1 bar−1), respectively. The best desalination performance (NaCl, MgSO4, and Na2SO4 rejections of 60.0%, 74.5%, and 92.0%, respectively) and As(III) removal (88.4%) along with satisfactory stability and reusability in cyclic continuous filtration was reported for PVA-SA-GO membrane. In addition, the PVA-SA-GO membrane indicated improved fouling resistance toward BSA foulant with the lowest flux decline of 7%.

Photo-Fenton reaction derived self-cleaning nanofiltration membrane with MOFs coordinated biopolymers for efficient dye/salt separation

Membrane technology has been widely used in textile industry for the separation of dye/salt mixtures. However, membranes inevitably suffered from the fouling issue, which greatly abated the water permeability and reduced the separation efficiency of membranes. Herein, a novel thin film nanocomposite (TFN) nanofiltration (NF) membrane was prepared by introducing photocatalytic sensitive material into the selective layer to directly degrade the foulants on the membrane surface. This functional selective layer was achieved by a complexation of carboxymethyl cellulose (CMC) and MIL-53 (Fe), which greatly enhanced the self-cleaning ability of the TFN membrane while MIL-53 (Fe) was served as nanofiller and photocatalyst simultaneously. The optimized TFN NF membrane modified with 0.5 mg CMC and 0.075 mg MIL-53 (Fe) exhibited a high pure water permeability of 39.83 L m−2 h−1 bar−1, while maintaining high dye rejections above 99.00 % for CR, G250 and MB. Meanwhile, the obtained membrane exhibited impressive rejections of salts (61.49 % for Na2SO4 and 17.22 % for NaCl). This simple fabrication strategy provided new insights to augment the separation performance of TFN NF membrane with self-cleaning ability in organic separation systems.

Addressing Specific (Poly)ion Effects for Layer-by-Layer Membranes.

Layer-by-layer (LbL) assembly of the alternating adsorption of oppositely charged polyions is an extensively studied method to produce nanofiltration membranes. In this work, the concept of chaotropicity of the polycation and its counterion is introduced in the LbL field. In general, the more chaotropic a polyion, the lower its effective charge, charge availability, and hydrophilicity. Here, this is researched for the well-known PDADMAC (polydiallyldimethylammonium chloride) and PAH (poly(allylamine) hydrochloride), and the synthesized PAMA (polyallylmultimethylammonium), with two different counterions (I- and Cl-). Higher chaotropicity (PDADMAC > PAMA-I > PAMA-Cl > PAH) translates into a reduced charge availability and a more pronounced extrinsic charge compensation, resulting in more mass adsorption and a higher pure water permeability. PAMA-containing membranes show the most interesting results in the series. Due to its molecular structure, the chaotropicity of this polycation perfectly lies between PDADMAC and PAH. Overall, the chaotropicity of PAMA membranes allows for the formation of the right balance between extrinsic and intrinsic charge compensation with PSS. Moreover, modifying the nature of the counterions of PAMA (I- or Cl-) allows to tune the density of the multilayer and results in lower size exclusion abilities with PAMA-I compared to PAMA-Cl (higher MWCO and lower MgSO4 retention). In general, the contextualization of the polyion interaction within the specific (poly)ion effects expands the understanding of the influence of the charge density of polycations without ignoring the chemical nature of the functional groups in their monomer units.

Mussel-inspired graphene oxide-based mixed matrix membranes for improving permeability and antifouling property

A multi-functional bio-inspired graphene oxide (GO) nanosheet was prepared firstly by successively modifying GO nanosheets with polydopamine (GO-PDA) and lysine (GO-PDA-LYS). Subsequently, the modified GO-blended polyvinylidene fluoride (PVDF) (PVDF/(GO-PDA-LYS)) MMMs were fabricated via non-solvent induced phase separation (NIPS) method. The presence of biomimetic GO-based nanosheets with good compatibility further improves the hydrophilicity of MMMs and endows them with favorable antifouling and antibacterial properties. The resultant MMMs show a competitive rejection rate (95.2%) of bovine serum albumin (BSA) and high pure water permeability of 850 L m-2h−1 bar−1, which is 7 times higher than that of the original PVDF membrane, as well as a high flux recovery ratio of over 80%. Moreover, the results of the Raman spectroscopy demonstrate that GO-PDA-LYS nanosheets are more evenly dispersed on the membrane surface than GO or GO-PDA nanosheets due to their better compatibility, thereby further improving antifouling and antibacterial performance of MMMs. This multi-functional biomimetic GO-PDA-LYS nanosheet provides new insights into an effective strategy for synchronously enhancing the water permeability, antifouling and antibacterial performance of MMMs.

Feasibility of hydrophilic polyethylene separator for membrane bioreactor for wastewater treatment: Fouling behaviors and cleaning

The increasing cost of polyvinylidene fluoride has motivated efforts of researchers to seek a cheap membrane material for membrane bioreactors (MBRs). An inexpensive hydrophilic polyethylene (PE) lithium-ion battery separator was used in this study to construct a flat-sheet membrane module for MBRs treating synthetic municipal wastewater (PE-MBR). The PE separator showed an interconnected and open pore structure with a pore size of 50–60 ​nm. Its hydrophilicity was confirmed by the contact angle (77.65°) and relatively high pure water permeability of 412.17 LMH. The operation of the PE-MBR under 15 LMH below the critical flux last more than 50 ​d before the trans-membrane pressure reached 25 ​kPa and the COD removal was higher than 90%. The revised Hermia model fitting suggested that cake formation was the predominant fouling mechanism on the PE separator with polysaccharides as the main organic pollutant. A cleaning efficiency of 76.26% of the PE separator was achieved using 1 ​g/L of Oxalic acid, 3 ​g/L of NaOH, and 100 ​mg/L of EDTA as the cleaning reagents. This study establishes the feasibility of the PE separator in MBRs and provides a new strategy to lower the operation cost and broaden the real applications of MBR in wastewater treatment.

High performance loose nanofiltration membranes with enhanced fouling-resistance by rapid covalent co-deposition of dopamine and diamine-zwitterion

Nanofiltration (NF) membranes have been extensively employed for the treatment of textile wastewater to produce clean water, due to their capability of retaining small organic molecules. In this study, zwitterionic loose nanofiltration (Z-NF) membranes have been successfully fabricated by the rapid co-deposition of dopamine and diamine-zwitterion (Z-DNMA) via covalent bonds. The fabricated Z-NF membranes show improved hydrophilicity and enhanced fouling-resistant ability due to the incorporation of the zwitterionic functionality. Following the systematic investigation on the ratio between dopamine and Z-DNMA as well as the co-deposition time, the identified optimum membrane (Z-NF3) exhibits a high pure water permeability (PWP) of 32.0 LMH bar−1 and high organic dye rejections of 99.7 % and 98.6 % for Congo red (CR) and methyl blue (MB), respectively. In addition, the fouling experiments of Z-NF3 show that the flux recovery ratios (FRRs) for the filtration of bovine serum albumin (BSA), sodium alginate (NaAlg), and CR are 99.1 %, 92.0 %, and 82.2 %, respectively, along with lower irreversible fouling ratios (Rir) and higher reversible fouling ratios (Rr) values compared to those of the control membrane. The high PWP and high rejections to organic dyes, coupled with its superior fouling-resistant performance, indicate its great potential for practical applications in the treatment of textile wastewater.

Efficient preparation of ultrathin ceramic wafer membranes for the high-effective treatment of the oilfield produced water

Efficient preparation of ceramic membranes helps to reduce costs and makes them more competitive in the field of wastewater treatment. In this work, an ultrathin Al2O3 ceramic wafer membrane with a thickness of 250 µm and the mean pore size of approximately 200 nm was prepared from the Al2O3/polysulfone slurries via a casting-phase inversion/sintering approach. This ultrathin and hydrophilic ceramic wafer has a fully sponge-like and slightly asymmetric structure and desirable porosity, endowing it with an exceptionally high pure water permeability of ∼ 45,000 L m-2h−1 bar−1, an ultrahigh and stable emulsion flux of 2500 ∼ 3500 L m-2h−1 bar−1, as well as a high oil rejection of 99 % against real oilfield produced water (OPW). In addition, the increased Al2O3 content enhanced the thermodynamic instability of the ceramic slurry, leading to the enhanced interfacial instability, which contributes to the uniform distribution of Al2O3 particles on the precursor membrane surface to some extent during the phase inversion process, thus to reduce the surface defects of ceramic membranes after sintering. The membrane fouling analysis revealed that the dominant fouling mechanism was cake filtration, indicating the formation of a relatively dense and smooth skin layer of the ceramic wafer, which endow it with a high flux recovery ratio of 97.8 % by a simple chemical cleaning after OPW filtration.

Preparation of Chemically Resistant Cellulose Benzoate Hollow Fiber Membrane via Thermally Induced Phase Separation Method.

For the first time, we have successfully fabricated microfiltration (MF) hollow fiber membranes by the thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) methods using cellulose acetate benzoate (CBzOH), which is a cellulose derivative with considerable chemical resistance. To obtain an appropriate CBzOH TIPS membrane, a comprehensive solvent screening was performed to choose the appropriate solvent to obtain a membrane with a porous structure. In parallel, the CBzOH membrane was prepared by the NIPS method to compare and evaluate the effect of membrane structure using the same polymer material. Prepared CBzOH membrane by TIPS method showed high porosity, pore size around 100 nm or larger and high pure water permeability (PWP) with slightly low rection performance compared to that by NIPS. On the contrary, CBzOH membranes prepared with the NIPS method showed three times lower PWP with higher rejection. The chemical resistance of the prepared CBzOH membranes was compared with that of cellulose triacetate (CTA) hollow fiber membrane, which is a typical cellulose derivative as a control membrane, using a 2000 ppm sodium hypochlorite (NaClO) solution. CBzOH membranes prepared with TIPS and NIPS methods showed considerable resistance against the NaClO solution regardless of the membrane structure, porosity and pore size. On the other hand, when the CTA membrane, as the control membrane, was subjected to the NaClO solution, membrane mechanical strength sharply decreased over the exposure time to NaClO. It is interesting that although the CBzOH TIPS membrane showed three times higher pure water permeability than other membranes with slightly lower rejection and considerably higher NaClO resistance, the mechanical strength of this membrane is more than two times higher than other membranes. While CBzOH samples showed no change in chemical structure and contact angle, CTA showed considerable change in chemical structure and a sharp decrease in contact angle after treatment with NaClO. Thus, CBzOH TIPS hollow fiber membrane is noticeably interesting considering membrane performance in terms of filtration performance, mechanical strength and chemical resistance on the cost of slightly losing rejection performance.

Organic solvent-free polyelectrolyte complex membrane preparation: Effect of monomer mixing ratio and casting solution temperature

The organic solvent-free aqueous phase separation (APS) process is a new and sustainable alternative to the conventional nonsolvent-induced phase separation (NIPS) process. However, low water permeability is a primary concern of such APS membranes. Herein, we introduced casting solution temperature and mixing ratio as two key parameters to improve the performance of poly (sodium 4-styrene sulfonate) (PSS) and branched Polyethylenimine (PEI) complex membrane prepared by pH shift-induced APS process. It was found that PSS-PEI monomer mixing ratios of 1:1.65 and 1:1.70 resulted in nanofiltration membranes with pure water permeability (PWP) of ∼4.5 and ∼8 LMHbar−1. The salt retention tests of these membranes showed higher divalent salt retention than monovalent salt following the order of MgCl2 > MgSO4 > Na2SO4 >NaCl. In comparison, PSS-PEI monomer mixing ratios of 1:1.75 and 1:1.80 led to the formation of ultrafiltration membranes with BSA retention of ∼98% and ∼36%, and PWP of ∼40 and ∼199 LMHbar−1, respectively. The variation of casting solution temperature also showed a significant influence on membrane morphology and performance. The increase in temperature from 25 to 60 °C resulted in ultrafiltration membranes with high BSA retention (>90%) and PWP in the range of ∼53–140 LMHbar−1. This sharp increase in PWP was attributed to the combined effect of the thinner skin layer and larger pore size of the membranes. Overall, this work demonstrated that casting solution temperature and monomer mixing ratio could be used as new tuning parameters for high-performance PSS-PEI membrane fabrication with excellent control over membrane structure and performance.